WO2007105598A1

WO2007105598A1 - Method for producing aluminate phosphor and aluminate phosphor

Info

Publication number: WO2007105598A1
Application number: PCT/JP2007/054558
Authority: WO
Inventors: Hidetoshi Saitoh; Shunsuke Tahara; Nobuyoshi Nambu; Atsushi Nakamura; Hiroshi Ito
Original assignee: Nagaoka University Of Technology; Chubu Chelest Co., Ltd.; Chelest Corporation
Priority date: 2006-03-10
Filing date: 2007-03-08
Publication date: 2007-09-20
Also published as: JPWO2007105598A1; EP2006348A4; CN101400758B; EP2006348A2; US20090047202A1; CN101400758A; JP5261667B2

Abstract

Disclosed is a novel aluminate phosphor which emits blue fluorescence with high color purity and high luminance in a certain wavelength range through ultraviolet light excitation and electron beam excitation. Also disclosed is a useful method for producing such an aluminate phosphor. Specifically disclosed is a method for producing an aluminate phosphor, which comprises a step wherein an aluminate represented by the following composition formula: 7(Sr1-xEux)O·yAl2O3 (wherein x and y satisfy 0 < x ≤ 0.5 and 1 ≤ y ≤ 36) is heated in a reducing atmosphere while being in contact with magnesium oxide.

Description

Specification

Process for producing aluminate phosphor and aluminate phosphor

Technical field

The present invention relates to a method for producing an aluminate phosphor, and to the aluminate phosphor produced by the method.

Background art

Phosphors having an aluminate as a mother structure are widely put into practical use as ultraviolet-excited phosphors that emit light mainly in a blue to green color tone region. In particular, recently, for plasma display panels (PDPs), development of vacuum ultraviolet ray excited light emitting devices having a mechanism for exciting a phosphor by the vacuum ultraviolet rays emitted by rare gas discharge to emit light has been actively conducted. ing. In fact, several aluminate phosphors have been put to practical use for PDPs that emit blue to green light.

[0003] By the way, the aluminate is represented by the composition formula: xMO. YAl 2 O (wherein, M is an alkaline earth metal)

twenty three

Which metal is represented). As the metal M, phosphors of various compositions are manufactured by introducing a plurality of divalent metals or doping an M site with a rare earth metal or Mn as an activator. For example, it has been confirmed that blue light is emitted by ultraviolet excitation when metal doped with Ba and Mg as metal M, and doped with Eu as an activator at the Ba site.

Among them, representative ones are, for example, BaM g Al 2 O 3: Eu disclosed in JP-B-52-22836, or BaMgAl 2 O 3: Eu disclosed in Japanese Patent Application Laid-Open No. 08-115673.

It is 2 16 27 10 17 mag. In addition to these, the ratio of Ba and Al to the above BaMgAl 〇: Eu is increased.

10 17

Or a part of Ba is replaced with Sr to suppress the thermal deterioration due to the baking treatment (Japanese Patent Laid-Open No. 2000-226574), an aluminate of a magnetoplumbite type structure, and an activator of Eu. What was added as (Japanese Patent Application Laid-Open No. 2001-240856) and the like are known.

Further, for example, BaAl:: Mn or BaMg in which aluminate is doped with Mn as an activator.

12 19

Al 2 O 3: Mn is known as a green phosphor that emits green fluorescence upon ultraviolet excitation

14 23

Ru. In addition, Ce and Tb activated lanthanum 'magnesium' to further enhance the light emission characteristics. A part of Ba in Zn-halide green phosphor (Japanese Unexamined Patent Publication No. H06-240252) or a manganese-substituted barium lumium aluminate phosphor is replaced with Zn, and the remaining Ba is replaced with Sr, Furthermore, a Ce--Mn co-activated green phosphor in which Ce is activated (Japanese Patent Laid-Open No. 2000-290647) is also known. As another phosphor, europium activated strontium aluminate exhibiting a bluish green color with an emission peak wavelength of 493 nm is also known.

Further, among the aluminate phosphors, there are so-called luminous phosphors having long-lasting properties. This phosphorescent phosphor is MAIO (wherein, M is selected from Ca, Sr and Ba)

Four

And at least one kind of metal element) is a parent structure. As such a luminescent phosphor, one in which Eu as an activator and another rare earth element as a coactivator are known (Japanese Patent Application Laid-Open No. 07-11250). Besides, a part of aluminum of the matrix aluminate is replaced with boron and contained to stabilize the crystal to improve the afterglow property (Japanese Patent Laid-Open No. 08-73845), the matrix is Sr Al O And you

Examples thereof include those obtained by adding 2 <11> <1> <1> <1> <1> <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< 212 << H <H 2000) to addition of dysprosium as a co- activation agent.

As described above, the conventional aluminate phosphor is composed of an oxide containing three or more metals, and in the production of these phosphors, the respective metal components are mixed uniformly. It becomes important whether they match.

By the way, most of the above-mentioned phosphors are manufactured by a method of obtaining a composite metal oxide by mixing and calcining a solid phase raw material so as to obtain a desired metal composition ratio, that is, by the classical method of solid phase method. It is done. In this solid phase method, a plurality of metal oxides are mixed in the solid phase state, so even if they are uniformly mixed, they are clearly heterogeneous phases when viewed microscopically. Also, no matter how carefully the metal composition ratio and the doping amount of the metal element are controlled, and even if the composition ratio of the metal component contained in each individual particle is controlled as desired, within the particle It is impossible in principle to produce phosphors in which the metal distribution is completely uniform.

Further, in order to manufacture a uniform composite metal oxide-based or aluminate-based phosphor composed of a plurality of metal oxides as described above, a precursor having a uniform composite metal composition as a precursor immediately before that is used. In order to obtain a uniform precursor substance, it is necessary to synthesize it from the point of raw material through a uniform state. Such methods include sol-gel method and coprecipitation There is known a liquid phase method which emphasizes a chemical method represented by the law.

However, even with these conventional liquid phase methods, if the composition ratio of the plurality of metal components is made uniform, the manufacturing cost will rise, and the manufacturing operation will be very complicated. In addition, even if the metal composition ratio in the solution state is uniform, the metal composition ratio of the obtained powder must be nonuniform. The hydrolysis rate and solubility product of the metal compound differ depending on the type of metal, and the metal composition ratio of the precipitate formed in the subsequent process such as hydrolysis, neutralization or precipitation becomes uneven. It is considered that such nonuniformity of the metal composition also has a considerable adverse effect on the fluorescence characteristics of the complex oxide-based or aluminate-based phosphors.

[0011] Under these circumstances, the present inventors have developed a technology described in WO 2005/090513 as a result of repeated research aiming at development of a novel aluminate blue phosphor. The present invention relates to a novel blue phosphor represented by Sr Al 2 O 3: Eu, which has various uses.

7 12 25

Development is expected. Since this phosphor has a light emission peak wavelength of 41 Onm, which is somewhat close to ultraviolet light, there is still room for improvement in its application to displays and three-wavelength fluorescent lamps. That is, if it is possible to give such a characteristic that it is desirable to bring the emission peak wavelength closer to the vicinity of 45 Onm, which is better in color purity, to be applied to these applications, the applications will be dramatically increased. Is a must.

Disclosure of the invention

The present invention has been made under such circumstances, and is a further development of the technology described in the above-mentioned WO 2005/090513 publication. The object of the present invention is to focus on an aluminate-based phosphor which has been confirmed to emit fluorescence by ultraviolet excitation and electron beam excitation, and to emit ultraviolet light which has a uniform composition and a higher degree of blueness, and emits fluorescence. The aim is to develop a new electron beam excited type aluminate phosphor. Another object of the present invention is to provide a method capable of efficiently producing such a phosphor.

The method for producing an aluminate phosphor according to the present invention is a composition formula: 7 (Sr Eu) 0-yAl O (

1-xx 2 3 In the formula, x, y is 0 <x ≤ 0.5, l ≤ y ≤ 36), and the reducing atmosphere in the state in which an anolamine salt is in contact with an acid manganate. It is characterized in that it includes the step of heating inside.

The aluminate phosphor of the present invention is produced by the above method, and is an ultraviolet ray. It is characterized by emitting light at an emission peak wavelength of 450 to 470 nm by excitation and electron beam excitation.

Brief description of the drawings

FIG. 1 is an emission spectrum diagram when the aluminate-based phosphor obtained in the example is irradiated with ultraviolet light with an excitation wavelength of 325 nm.

BEST MODE FOR CARRYING OUT THE INVENTION

First, the method for producing a phosphor according to the present invention will be described in more detail.

The composition formula used in the method of the present invention: 7 (Sr Eu) 〇'yAl〇

-x 2 3

And the range of the Eu doping amount (X) to Sr is “0 <χ≤ 0 · 5”, the ratio of alumina (A10)

twenty three

The range of (y) is the range of “1≤y≤ 36”.

When the above-mentioned Eu doping amount (X) is zero (0), that is, without Eu doping, the luminescence center is lost and no light emission is shown, while the Eu doping amount is too high and the value of (X) is 0 When it exceeds 5, concentration quenching occurs and the decrease in luminance becomes noticeable. Therefore, in the present invention, the value of (X) is determined as described above. A more preferable range of (X) is the range of “0. 001 ≤ x ≤ 0.3”, and the highest light emission characteristic is exhibited in this range.

On the other hand, when the ratio (y) of Al 2 O is less than 1, the function as a phosphor decreases and satisfactory fluorescence is obtained.

twenty three

If (y) exceeds 36 and becomes too high, satisfactory fluorescent characteristics will not be exhibited again. Therefore, in the present invention, the value of (y) is set in the above range. The more preferable range of (y) is the range of “3≤y≤27”, and the highest light emission characteristic is exhibited in this range

The aluminate represented by the compositional formula: 7 (Sr Eu) 0 -yAl 2 O has the following properties: (1) Sr, Eu and Al

l-x x 2 3

It can manufacture via the process of manufacturing the powder which consists of an organometallic chelate used as a metal component, and the process of baking the powder obtained at (2) said process (1), and obtaining an aluminate. More detailed production conditions are disclosed in the above-mentioned WO 2005/090513. Specific production conditions are not particularly limited, but it is easier to use the organometallic chelate powder in which each metal component consisting of Sr, Al and Eu is uniformly mixed at the molecular level as a precursor. The aluminate strontium represented by the formula can be obtained.

Here, the organic metal chelate powder to be a precursor is each metal compound and an organic chelating agent. The aqueous solution can be easily obtained, for example, by spray-drying after being mixed so as to obtain a predetermined metal composition ratio to obtain a clear organic metal chelate aqueous solution.

Specifically, the following method is exemplified. First, a powder containing organometallic chelates of Sr, Eu and A1 is produced. This manufacture is performed, for example, as follows. First, Sr and Eu are precisely weighed so as to obtain a predetermined metal composition, and these are reacted with an organic chelating agent to prepare a clear organic metal chelate aqueous solution. This reaction is carried out in an aqueous medium, for example, at a temperature of 20 ° C to boiling point, preferably 50 to 70 ° C. The preferred aqueous solution concentration is 5% by mass or more and 30% by mass or less, more preferably 10% by mass or more and 20% by mass or less in terms of solid content conversion, but of course it is not limited to this temperature range.

[0023] The amount of the organic chelating agent used is preferably at least 1.0 times mol and not more than 1.5 times mol based on the metal ion so that all the metals can be completely dissolved. . In the case where the metal chelate or the organic chelating agent is not completely dissolved, in the case where ammonia or an amine is added, it is preferable to completely dissolve it. Alternatively, the organic metal chelates of the above-mentioned respective metals may be prepared separately, and they may be precisely weighed and mixed so as to obtain a predetermined metal ratio.

Particularly preferred in the present invention, which uses carbonates, nitrates, hydroxides, oxides, etc., as metal raw materials, in the present invention using strontium and europium, has good reactivity and excess ions after the reaction. It is an oxide or carbonate in which etc. do not remain. As for aluminum, considering the reactivity with organic chelating agents, usable raw materials are substantially limited to salts, sulfates and nitrates, and nitrate is preferred. Among them, it is particularly preferable to first produce an aluminum chelate solution using chloride, sulfate or nitrate, pre-produce high purity aluminum chelate crystals by crystallization, and use this as an aluminum source. .

By the way, what matters most when producing an aluminate phosphor is the mixing of impurity elements. Among the organic metal chelates, sodium salts and potassium salts remain in the fluorescent body even after thermal decomposition, and they should not be used because they cause the composition of the fluorescent body to be upset. In addition, organic acids such as hydrochloric acid, sulfuric acid, phosphoric acid or their salts, etc. and inorganic acids and inorganic acid salts containing chlorine, sulfur or phosphorus, etc .; and thiol compounds are preferably not used as much as possible. These are almost completely pyrolyzed in the firing process, but complex metal chelates of uniform composition Because there is a risk of adversely affecting the generation of

Examples of the organic chelating agent used in the present invention include ethylenediamine tetraacetic acid, 1,2-cyclohexanediamine tetraacetic acid, dihydroxyglycine, diamineopropanoltetraacetic acid, diethylenetriaminepentaacetic acid, ethylenediamine diacetic acid and ethylenediamine Dipropionic acid, Hydroxyethylenediamine triacetic acid, Glycoletherdiamine triacetic acid, Hexamethylendiaminetetraacetic acid, Ethylenediamine di (o-hydroxyphenyl) acetic acid, Hydroxye noreimino diacetic acid, Iminoniacetic acid, 1,3-Diaminopropane Tetraacetic acid, 1,2-Diaminopropane tetraacetic acid, 2-tri-portal triacetic acid, 2-tri-portal 3-propionic acid, triethylenetetramine hexaacetic acid, ethylenediamine dibasic acid, 1,3-diaminopropane dibasic acid, glutamate mono-N, N — Diacetic acid, gas There may be mentioned water-soluble aminocarboxylic acid-based chelating agents such as paraformic acid-N, N-diacetic acid and the like. Any of these monomers, oligomers or polymers can be used. As the organic chelating agent, more preferably, an aminocarboxylic acid chelating agent and / or a salt thereof is used.

More preferably, as the organometallic chelate, a complex composed of an aminocarboxylic acid chelating agent and a metal ion, and / or a salt thereof is used. Further, as the aminocarboxylic acid chelating agent, more preferably, at least one selected from the group consisting of ditritrichloroacetic acid, ethylenediamine tetraacetic acid, diethylenetriaminepentaacetic acid, and triethylenetetramine hexaacetic acid is used.

However, the free acid type, ammonium salt or amine salt is used, and the chelate formation constant with each metal, the stability of the metal chelate, and the solubility of the metal chelate in water or alkaline aqueous solution are taken into consideration. It is desirable to select an appropriate one for each metal component to be used.

The organic metal chelate aqueous solution prepared as described above is then powdered by spray drying. The conditions for spray drying may be appropriately set according to the concentration of the aqueous solution, the solution processing rate, the amount of air for spraying, the amount of air for hot air, etc. The drying temperature is preferably the temperature at which the organic substance is not decomposed. Also, a temperature sufficient to dry sufficiently may be employed. From this point of view, the drying temperature is generally in the range of 140 to 180 ° C., more preferably in the range of about 100 to 200 ° C. Considering such drying temperatures, the above amino acids used in the present invention are It is desirable to select the one that does not thermally decompose at a temperature of about 200 ° C. or less as the rubonic acid-based chelating agent.

The organometallic chelate powder obtained as described above is then fired to form a metal oxide. The preferable conditions at this time are as follows. When the organic metal chelate powder obtained as described above is fired as it is, the organic component is thermally decomposed to form a complex oxide powder. In the firing, when the organic components are completely decomposed, for example, at 500 ° C. or higher, all the organic components are decomposed and burned off to form a composite metal oxide. The crystallinity of the composite metal oxide is improved as the calcination temperature is raised, so that the calcination can be carried out at a temperature of up to 1600 ° C. if necessary.

The atmosphere for firing and heating is not necessarily in the air, and may be performed in an oxygen-enriched atmosphere, a neutral atmosphere, or a reducing atmosphere, as necessary. Preferably, it is fired in an atmosphere containing at least one selected from the group consisting of air, oxygen and nitrogen.

When the aluminate powder obtained as described above is brought into contact with magnesium oxide and heated in a reducing atmosphere while maintaining the contact state, the aluminate phosphor according to the present invention is obtained. The shape of the magnesium oxide used herein is not particularly limited. For example, coarse particles, fine particles, thin films, substrates and the like can be used. Also, they may be single crystals or polycrystals.

When the above-mentioned aluminate powder and the above magnesium oxide are heated in a reducing atmosphere while maintaining the contact state, magnesium oxide of magnesium oxide becomes an aluminate powder at the contact interface between the aluminate powder and the magnesium oxide. Thermal diffusion. The resulting phosphor has a crystal structure clearly different from that of the strontium aluminate phosphor disclosed in the above-mentioned WO 2005/090513. That is, according to the method of the present invention, a novel blue phosphor having a novel crystal structure and composition and emitting specific fluorescence at an emission peak wavelength of 450 to 470 nm is obtained.

The heating conditions at this time may be heating the precursor powder in a contact state in a reducing atmosphere, and the preferable heating temperature is 500 ° C. or more and 1600 ° C. or less, more preferably 800 ° C. or more and 1500 ° C. C or less, more preferably in the range of 800 ° C. or more and 1500 ° C. or less. Although the reducing atmosphere is not particularly limited, it is preferable to use an argon / hydrogen mixed atmosphere or nitrogen / water. It is an elementary mixed atmosphere.

[0035] According to the manufacturing method of the present invention described above, by using, as the precursor, a powder containing an organic metal chelate uniformly mixed at the molecular level as a raw material, a phosphor having a uniform composition at the molecular level is obtained. Efficient and reliable manufacturing.

The aluminate phosphor of the present invention is produced by the above-mentioned method of the present invention, but the composition formula after thermal reduction has not been clarified until now. Force This heat-reduced product exerts a specific fluorescence characteristic to generate blue emission of high color purity which emits light specifically at an emission peak wavelength of 450 to 470 nm by ultraviolet excitation and electron beam excitation as described above.

[0037] The phosphor of the present invention produces blue light with a specific high color purity at an emission peak wavelength of 450 to 470 nm as described above, but its fluorescence lifetime is extremely short. This is in contrast to the very long or afterglow fluorescence lifetime of the strontium aluminate phosphor disclosed in the prior art cited above.

[0038] The metal composition ratio and structure of the phosphor according to the present invention have not been clarified at present. According to the results of X-ray diffraction analysis of the phosphor of the present invention obtained by thermal reduction, the possibility of coexistence of multiple phases is also fully considered. However, the crystal structure is clearly different from the strontium aluminate phosphor disclosed in the prior art mentioned above, and both should be classified as completely different phosphors.

Example

The present invention will be described in more detail by way of examples and test examples below, but the scope of the present invention is not limited to these.

Example 1

After adding 217 g of ethylenediaminetetraacetic acid and water to a 1 liter beaker to make the total amount 500 g, 100 g of aqueous ammonia was added and dissolved. While this was stirred, 110 g of strontium carbonate was slowly added, and the temperature was raised to 100 ° C. and stirring was continued for 2 hours to completely dissolve it. Water was added to this solution to adjust its concentration to obtain a colorless and transparent aqueous solution of strontium tetramethylenediacetic acid (Sr-EDTA) complex.

On the other hand, 0. 65 g of ethylenediaminetetraacetic acid and water were added to a 100 ml beaker to make the total amount 10 Og, and 0.3 g of ammonia water was then added and dissolved. While stirring this, you After 0.4 g of oral palladium was added and the mixture was stirred at 80 ° C. for 30 minutes, it was completely dissolved to obtain a colorless and transparent solution of europium-ethylenediamine tetraacetic acid (Eu-EDTA) complex.

[0042] beaker 100 ml, obtained in the above Sr-EDTA complex solution 29. 72 g (Sr content: 4.41 mass ^_0/0) and Eu-EDTA complex solution 10. 55 g (Eu content: 0.440 mass ⁰ / ₀ ) and ethylene diamine tetraacetic acid ammonium (EDTA. 1 ·)) 9. 91 g (Al content: 7. 13

Four

After precisely weighing and mass-producing), water was added to make the total amount 100 g. Next, it is stirred for 30 minutes and completely dissolved, and the metal composition ratio is (Sr + Eu) / Al = 7/12, EuZSr = 0.2 / 0.0.98 colorless and transparent (Sr, Al, Eu) _ EDTA complex An aqueous solution was obtained.

This solution was powdered by a spray drying method at a drying temperature of 160 ° C. to obtain (Sr, Al, Eu) -EDTA complex powder. An X-ray diffraction chart of this powder was confirmed, and it showed a halo figure due to scattering of incident X-rays, and the crystal structure was amorphous.

The complex powder was calcined at 800 ° C. for 3 hours in an open-air electric furnace to thermally decompose and remove the organic matter, to obtain an aluminate powder. The obtained aluminate powder 0. Olg is dispersed in ethanol, dropped onto a (100) oriented magnesium oxide substrate (10 mm x 10 mm) and dried, and then in a stream of Ar + H (3%) By heating and reducing at 1400 ° CX for 24 hours

2

A phosphor film was produced.

The emission spectrum of this phosphor film when it is irradiated with ultraviolet light at an excitation wavelength of 325 nm is shown in FIG. As apparent from this figure, it can be seen that it emits blue light with high color purity and high luminance, with an emission peak wavelength of 450 to 470 nm. The emission spectrum by electron beam excitation with an acceleration voltage of 30 kV was also confirmed to be the same spectrum as FIG. 1, and it was confirmed that it is a blue phosphor applicable to both ultraviolet excitation and electron beam excitation.

Industrial applicability

The aluminate-based phosphor of the present invention is used as a blue phosphor such as a three-wavelength fluorescent lamp using an ultraviolet ray as an excitation source, a brama display, etc., and a cathode ray tube or a fluorescent display tube using an electron beam as an excitation source. It can be very effectively used as a phosphor to be used.

Further, according to the production method of the present invention, a blue phosphor having the above-mentioned characteristics can be efficiently produced, and can be provided as a phosphor which can be widely and effectively utilized for various applications.

Claims

The scope of the claims

[1] Composition formula: 7 (Sr Eu) 〇 'y Al ((wherein, x, y represent 0 <x ≤ 0.5, l ≤ y ≤ 36)

1-x 2 3

A process for producing an aluminate-based phosphor, comprising the step of heating the aluminate described in the foregoing in a reducing atmosphere in contact with magnesium oxide.

[2] The process according to claim 1, wherein at least one selected from the group consisting of balta-like, powder, and substrate-like single crystals and multiple crystals is used as the magnesium oxide.

[3] Said compositional formula: 7 (Sr Eu) '' y Al ((wherein, X, y are 0 <x ≤ 0.5, 0 <v ≤ 10

1-x x 2 3

The aluminate shown in

(1) producing a powder comprising an organic metal chelate having Sr, Eu and A1 as a metal component,

(2) a step of calcining the powder obtained in the step (1) to obtain an aluminate;

The manufacturing method of Claim 1 or 2 manufactured through.

[4] In the step (1), the metal simple substance of the constituent metal element or the metal compound thereof and the organic chelating agent, and / or the organic metal chelate of the constituent metal element are mixed to obtain a predetermined metal composition. The method according to claim 3, wherein the powder obtained by spray-drying the prepared clear organic metal chelate aqueous solution is used.

[5] The process according to claim 3 or 4, wherein an aminocarboxylic acid chelating agent and Z or a salt thereof are used as the organic chelating agent.

[6] The method according to [5], wherein the aminocarboxylic acid chelating agent is at least one selected from the group consisting of ditrilic triacetic acid, ethylenediamine tetraacetic acid, diethylenetriaminepentaacetic acid, and triethylenetetramine hexaacetic acid. Manufacturing method.

[7] The process according to any one of [3] to [6], wherein a complex composed of an aminocarboxylic acid chelating agent and a metal ion, and Z or a salt thereof are used as the organic metal chelate.

[8] The method according to any one of claims 3 to 7, wherein in the step (2), firing is performed in an atmosphere containing at least one selected from the group consisting of air, oxygen and nitrogen.

[9] The process according to any one of claims 3 to 8, wherein in the step (2), the firing is performed in the range of 500 to 1600 ° C.

[10] As the reducing atmosphere, a mixed gas of nitrogen and hydrogen or a mixed gas of argon and hydrogen The manufacturing method in any one of Claims 1-9 employ | adopted.

[11] The process according to any one of claims 1 to 10, wherein the heating is performed in the range of 800 to 1500 ° C.

[12] The method according to any one of [1] to [11], which is characterized by emitting light at an emission peak wavelength of 450 to 470 nm by ultraviolet excitation and electron beam excitation. Aluminate-based phosphors.

[13] The aluminate fluorescent material according to claim 12, wherein X, y force S, 0. 001 <x ≤ 0.3, 3 ≤ y ≤ 27 within the above composition formula.